Hundreds of people gathered in Philadelphia Tuesday to celebrate a new postage stamp with the image of Richard Allen, one of the country's first civil rights leaders whose story is not well-known by most Americans — even in the city he adopted as his home.

Allen, born into slavery in 1760, worked on a Delaware plantation until his master, moved by his preaching, allowed him to buy his freedom. Eventually, Allen came to Philadelphia and became a preacher at St. George's Episcopal Church. However, his black parishioners were forced to worship in a separate area from whites, so Allen and another black Methodist preacher, Absalom Jones, started a new church at the turn of the 19th century. 

"Make no mistake, the civil rights movement started that day when Richard Allen and Absalom Jones walked out of that church," said Richard Lawrence, a descendant of Allen's. 

The site of the men's first church, Mother Bethel AME on Sixth and Lombard streets in Philadelphia, has remained the same, although it was rebuilt four times to accommodate growing membership. The church was used to prepare black soldiers for the War of 1812 and also served as a stop on the Underground Railroad. Allen died a bishop of the AME church in 1831 and he is buried at Mother Bethel, along with his second wife, Sarah Bass Allen. 

Over the centuries, the church has grown to become a Christian denomination with 2.5 million members around the world.

On the same site where Allen eulogized George Washington in 1799, a standing-room-only crowd celebrated his contribution to their faith and to American history on Tuesday afternoon with spirited singing, prayers and speeches. 

Jackie Dupont-Walker, director of social action for AME International, led the campaign to get Allen's portrait on a forever stamp.

"It's good to finally see everyone understand, even those of us who have been AME, who have been proud, to really understand what we are now called to do," she said. "It's a call to action for us."

A common refrain among the speakers, clergy and lay people alike, was that the stamp should encourage more people to learn about the man called one of America's black founding fathers who influenced civil rights leaders in future generations including Frederick Douglass and Martin Luther King Jr.

"And this is not African-American history, it's American history," said Philadelphia Mayor Jim Kenney to applause. 

The Richard Allen stamp is the 39th in the U.S. Postal Service's black heritage series.